Traffic on the northbound and southbound lanes of the 110 Harbor Freeway starts to stack up during rush hour traffic on Feb. 5 in Los Angeles. / Kevork Djansezian, Getty Images

by Larry Copeland, USA TODAY

by Larry Copeland, USA TODAY

After nearly two years of sharp declines, traffic congestion in the USA is on the rise again, thanks largely to an improving economy.

For the first three months this year, congestion is up 4% compared with the same time last year, INRIX, a Kirkland, Wash.-based firm that provides traffic information and driver services, says in its annual Traffic Scorecard, which will be published Wednesday.

The uptick in the first quarter of this year follows a 22% drop in congestion in 2012 compared with 2011. This is the first such consecutive monthly increase in two years, and it parallels a steady increase in employment, which is up 1.3% for the year, INRIX says.

This year's upward trend and last year's decrease were both tied to the economy and to political wrangling in Washington, D.C., according to INRIX.

"In 2012, what we saw was a stop and go situation, where a tax and fiscal deadline, combined with fluctuations in employment, had a detrimental impact on traffic congestion," says Jim Bak, INRIX's director of community relations. "As consumers and businesses took a wait-and-see approach, employers were slowing hiring, consumers were not spending, that all had an impact on congestion."

Adie Tomer, an associate fellow specializing in transportation at the Brookings Institution, agrees with the economic portion of that analysis. "Infrastructure usage correlates with economic growth patterns," he says. Tomer notes that traffic congestion is still well below pre-recession levels; he says that while it has rebounded somewhat, there has been "a fundamental shift" in traffic congestion as people who have dropped out of the labor force have curtailed their driving. It's unknown if that shift is permanent, he says.

So far this year, 61 of the nation's 100 worst traffic cities have seen increases in congestion over last year, INRIX says; for all of 2012, just six of those cities saw increases over the previous year.

The city with the largest increase through the first quarter of this year is Boston, where congestion is up 30% from last year. "That's a perfect example of how the economy affects traffic," Bak says. "Unemployment figures there were 1.2 percentage points lower than the national average in February."

In February, the Texas Transportation Institute quantified the cost of congestion for 2011: Traffic snarls that year caused U.S. motorists to spend an additional 5.5 billion hours on the road and purchase an extra 2.9 billion gallons of fuel for an annual congestion cost of $121 billion.

INRIX found that, on average, the worst times to be on the roads in terms of delay are 7-8 a.m.and 4-5 p.m. during the week. The busiest morning commute hour is 8-9 a.m. on Tuesday; the busiest evening commute hour is 5-6 p.m. on Friday.

To compile its annual Traffic Scorecard, INRIX collects real-time data from about 100 million vehicles traveling the roads daily, and from state department of transportation sensors embedded in the road in each state. The firm then compares that data with information in its historical archives and runs an analysis for the report.

A factor not influencing traffic so far this year: pain at the pump.

"The one thing we've not had come into play at all this year is fuel prices," Bak says. "They've remained relatively stable."

INRIX cautions that a significant rise in unemployment in the second quarter, or another round of Washington paralysis could slow or stall the rise in congestion. "Where we go from here is entirely dependent on where things go with employment and what our government does with some of these issues," Bak says.